1. Field of the Invention
This invention relates to a heating apparatus which is installed in, for example, a low pressure CVD system and is suitable for heat treatment on wafers.
2. Description of Related Art
As is commonly known, a semiconductor integrated circuit manufacturing process involves a variety of IC process units, including oxidation and dispersion equipment, vapor phase epitaxial growth systems, low pressure CVD systems (LPCVD systems), and annealing equipment. These units are equipped with heating apparatuses for heat-treating silicon wafers (hereafter, simply referred to as “wafers”) on which IC's are being formed or to be formed.
FIG. 2 is a schematic diagram illustrating an example of vertical low pressure CVD systems equipped with a heater based on electric resistance heating as heating apparatus, for the purpose of explanation of prior arts. In low pressure CVD, films are generally formed at temperature of 400 to 800° C. under pressure of 0.1 to 30 Torr (approx. 0.013 kPa to 4.0 kPa).
As shown in FIG. 2, the batch processing vertical low pressure CVD system is provided with a reactor 51 made of quartz having circular hollow cross-sections and dome-shaped top; a cylindrical inner tube 54 made of quartz placed inside the reactor 51; a boat 53 which is placed inside the inner tube 54 and is mounted with a large number (for example, 100 to 150 or so) of vertically arranged wafers 52; and a manifold 56. The vertical low pressure CVD system is further provided with a cylindrical heater 55 concentrically placed around the reactor 51 so that the reactor is encircled with the heater in the case of this example. The reactor 51, the inner tube 54, the boat 53, and the heater 55 are arranged with the axis common thereto. On the manifold 56, the reactor 51 and the inner tube 54 are placed, and further, the boat 53 is placed with a pedestal (not shown) in-between. The manifold 56 is provided with gas injectors 57a and 57b for feeding source gas or the like into the inner tube 54 and with a gas exhaust port 58 for letting out reacted gas or unreacted gas from the reactor 51.
An explanation is given below about a case where, for example, a polysilicon film is formed on wafers 52 using the vertical low pressure CVD system provided with the heater 55 based on electric resistance heating. First, wafers 52 are set on the boat 53, and the boat 53 is inserted into the inner tube 54 from an opening (not shown) located at the lower end of the manifold 56, together with the pedestal (not shown) with the boat 53 placed thereon. The opening in the manifold 56 is closed with a hatch (not shown). Then the space inside the inner tube 54 is heated to a specified temperature by means of the heater 55 based on electric resistance heating, and further, silane gas is fed into the inner tube 54 through the gas injector 57a. The silane gas is heated and pyrolytically decomposed on the surfaces of the wafers 52, and a polysilicon film is thereby formed on the surfaces of the wafers 52. The reacted gas or unreacted gas goes through the path between the inner tube 54 and the reactor 51 and externally discharged from the gas exhaust port 58. As mentioned above, to form films on wafers in the vertical low pressure CVD system, the heater 55 based on electric resistance heating is used as heating apparatus for heat-treating the wafers 52.
FIG. 3 is a schematic diagram illustrating an example of single wafer processing vapor phase epitaxial growth systems equipped with infrared lamps as heating apparatus, for the purpose of explanation of prior arts. The details of the vapor phase epitaxial growth of silicon vary depending on source gas used (four varieties of gases: silicon tetrachloride gas, silane dichloride gas, silane trichloride gas, and silane gas), but in general the reaction occurs at a temperature of 1100 to 1200° C. or so.
As shown in FIG. 3, a disk-like susceptor designed to support a wafer 62 placed thereon one by one is placed in a reactor 61 made of quartz. The surface of the susceptor 63 is made of a graphite base material coated with silicon carbide. A plurality of infrared lamps 64 as heating apparatus is placed concentrically with the reactor 61 outside the reactor. In the upper space 61a in the reactor 61, source gas (including dopant), fed in through a gas feed port 65 together with hydrogen gas as carrier gas, moves in substantially laminar flow over the surface of the wafer 62, and is discharged from an exhaust port 66 located on the opposite side. In the lower space 61b in the reactor 61, hydrogen gas as purge gas is fed under a higher pressure than that of the source gas (reactive gas). In this vapor phase epitaxial growth system, a wafer 62 placed in the reactor 61 is radiantly heated to a specified temperature through the reactor 61 by means of infrared lamps 64 located above and beneath the reactor 61, and thus a silicon epitaxial layer is formed by vapor phase growth. As mentioned above, to form a silicon epitaxial layer in this vapor phase epitaxial growth system by vapor phase growth, infrared lamps 64 are used as heating apparatus for heat-treating the wafer 62.
FIG. 4 is a schematic diagram illustrating an example of single wafer processing vapor phase epitaxial growth system equipped with a high-frequency induction coil as heating apparatus, for the purpose of explanation of prior arts.
As shown in FIG. 4, a disk-like susceptor 73 made of graphite on which a wafer 72 is to be placed one by one is placed in a reactor 71 made of quartz. A high-frequency induction coil 74 for causing the susceptor 7 with a wafer 72 supported thereon to produce heat and thereby heating the wafer 72 is installed under the susceptor 73 outside the reactor 71. The high-frequency induction coil 74 and the susceptor 73 form a heating apparatus for heating a wafer 72. In the reactor 71, source gas (reactive gas) or the like is fed through a gas feed port 75. The gas or the like moves in substantially laminar flow over the surface of the wafer 72, and is discharged from an exhaust port 76 located on the opposite side. In this vapor phase epitaxial growth system, a wafer 72 is heated to a specified temperature by causing the susceptor 73 to produce heat via the high-frequency induction coil 74, and a silicon epitaxial layer is formed by vapor phase growth. As mentioned above, to form a silicon epitaxial layer in this vapor phase epitaxial growth system by vapor phase growth, the high-frequency induction coil 74 and the susceptor 73 made of graphite are used as heating apparatus for heat-treating a wafer 72.
However, in the above-mentioned heating apparatuses wherein heating is provided by radiant heat or conductive heat from a heater, there is restriction due to thermal conduction between the output of the heater and wafers as objects to be heated. As shown in Table 1, therefore, these apparatuses are theoretically unsuitable for rapidly raising or lowering the temperature. Thus, these apparatuses have a disadvantage that it takes much time to rise and lower the temperature of wafers and this leads to impaired throughput.
TABLE 1Required CharacteristicsRapidConventionalHigh-volumeTemperaturetemperatureApparatusesprocessinguniformityrise/dropHeater◯◯ΔLampX◯⊚High-frequencyX◯⊚induction coil⊚: Excellent Δ: Considerably restricted ◯: Medium X: Unsuitable 
In the above-mentioned heating apparatuses wherein radiant heating is implemented by infrared lamps, the performance greatly depends on the distance between the lamps and wafers as objects to be heated. Therefore, tens of lamps are required for several wafers. As shown in Table 1, these apparatuses have a disadvantage that the apparatuses are incapable of processing wafers in high volume. In the above-mentioned heating apparatuses wherein heating is implemented by a high-frequency induction coil, the susceptor caused to produce heat to heat wafers is formed in disk shape, and such apparatuses are so designed that wafers are placed on the disk-shaped susceptor. Therefore, these apparatuses have a disadvantage that they are incapable of processing wafers in high volume.